Why would Macbeth take issue with Banquo and young son Fleance What does his intention reveal about Macbeth and state of mind at this point in the play?

At this point in the play, Macbeth is troubled and confused. He is afraid of Banquo--"My fears in Banquo stick deep"--because Banquo knows about the witches's predictions and may suspect (and in fact does) that Macbeth murdered Duncan. The murder has made him into an insomniac and a paranoid, and he asks himself if it was worth it. Well, he is pretty sure that it wasn't. So it annoys him that the benefit of the murder, such as it is, will not extend beyond his lifetime. Therefore, since he is annoyed that he has made "the seed of Banquo kings" he hopes to frustrate the prophecy by killing Fleance. But this is ridiculous--he cannot benefit his own children because he doesn't have any. Murdering Fleance will not help matters. But Macbeth is hardly rational at this point (or indeed at any point after he kills Duncan)